The goal of this project is the determination of the three-dimensional structures, at atomic resolution, of every kinetically-significant step in the mechanistic pathway of the glycolytic enzyme triose phosphate isomerase. The structures will be determined by the method of X-ray diffraction; those complexes not normally stable at ordinary temperatures will be studied at sub-zero temperatures, where their lifetimes are long enough for data collection. Single crystals of the enzyme from yeast have been grown by precipitation with polyethylene glycol, and a structure solution is in progress at 2A resolution. We plan to add the substrate dihydroxyacetone phosphate to the crystals at minus 10 degrees C and collect a complete set of high resolution diffraction data on the Michaelis complex. The crystal structure of a productive enzyme-substrate complex should add greatly to our knowledge of the origin of the catalytic power of enzymes.